1. Field of Invention
This invention relates to in situ testing of vehicle suspension damping components such as automobile shock absorbers and McPherson struts.
2. Description of Prior Art
Modern automobiles generally have excellent handling characteristics when they are new. (Note that the terms automobile, car and vehicle are used interchangeably in this specification.) These characteristics have been designed into the car with a great deal of effort by the automotive engineers, taking into consideration the masses of the car, the spring and tire resiliences, and the damping factors of the shock absorbers, also called shocks and struts, and other dynamic and linkage elements of the suspension system. One of the most frequently encountered handling problems experienced by car owners as the new car is driven and becomes worn or abused, is caused by shock absorber or MacPherson strut deterioration. Deterioration of these motion damping elements destroys the handling characteristics of a car, however repair of problems cause by faulty shock absorbers is simple to perform by replacement once the problem has been identified. But therein lies the problem.
The most common method for checking the performance of shock absorbers is for the owner or mechanic to jump up and down on the car bumper and observe whether or not the car motion appears to be adequately damped. When the shocks are completely worn out, it is clear that the damping is inadequate, however by the time the wear is readily observable, the car owner has been driving for an extended period of time with bad shocks. By then the owner has learned to hate his vehicle, the tires have been abnormally worn, and the roadability has deteriorated to the point that he or she has been driving dangerously all over the road.
Conscientious and honest mechanics will `test` the shocks individually by disconnecting one end and manually pulling and pushing to judgmentally observe the level of damping resistance. Disconnecting the shock can be an expensive proposition on many cars. These methods of jumping on the bumpers and of pulling and pushing on disconnected shocks are highly subjective and unreliable except for the cases where the shocks are completely worn out. Frequently mechanics will point out the shiney spots where suspension elements may have `bottomed out` and indicate that new shocks are needed, usually leaving the customer wondering whether he is getting a correct diagnosis. Leaky hydraulic shocks are more easily identified in that the leaks usually can be identified by observation.
Despite the fact that this problem has been in existence since the advent of the automobile, an economic, technically valid method is not available today for the ordinary garage mechanic to determine whether the shocks on a car have degraded to the level that replacement is necessary or advisable except for the completely inoperative shocks.
U.S. Pat. No. 1,891,613, `Method of and Apparatus for Testing the Riding Qualities of Vehicles Issued Dec. 20, 1932 is the prior art which is most pertinent to our invention. Our invention differs from that invention in five specific areas:
1. Our invention incorporates an improved, inexpensive car raiser and dropper method;
2. Our invention specifically measures the motion of the vehicle body with respect to the wheel, which is also where the shock absorbers are mounted.
3. Our invention incorporates an inexpensive wheel-mounted car body motion sensor and recording method with enough sensitivity to detect and display minor and major shock degradation including sometimes subtle differences between front and rear shock performance.
4. Our invention provides an alternate improved wheel mounted method for motion sensing for use with an external prior art readout recorder or other visual display or for use in conjunction with a computer or special test equipment.
5. Our invention incorporates a continuously updated library of baseline performance curves for different vehicles (including old and new vehicles, front and rear), said library being available as transparent overlays, or in a computer data base amenable for electronic display or paper printout.
Primary emphasis for this invention is placed upon providing functional simplicity coupled with effective performance measurement in an economical manner. The approach includes other options which may be preferable from the view point of operational ease and time saving although more expensive.
Other prior art patents related to shock absorber testing which were reviewed include:
U.S. Pat. No. 2,716,883 Testing Machine for Shock Absorber or the Like, Sep. 6, 1955 PA0 U.S. Pat. No. 2,934,940 Means for Testing Shock Absorbers, May 3, 1960 PA0 U.S. Pat. No. 2,923,147 Shock Absorber Tester, Feb. 2, 1960 PA0 U.S. Pat. No. 4,376,387 Dynamic Shock Absorber Evaluation, Mar. 15, 1983.